README: Add blurb about enabling the UART on the Mac

Signed-off-by: Marc Zyngier <maz@kernel.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/README b/README
index 11bf50c..eed6794 100644
--- a/README
+++ b/README
@@ -254,3 +254,24 @@ board is using, as well as the CC line used, the pin set used for
 serial, and potentially the debug status. The HW supports two boards
 being driven by a single Pico (see the HW documentation for the gory
 details).
+
+** Software configuration on the Mac itself
+
+It is all good to have a serial port, something needs to interact with
+it on the Mac as well.
+
+- As far as I understand, MacOS doesn't directly provide a driver for
+  the UART. It is apparently possible to enable it, but I can't help
+  you with that.
+
+- If running m1n1 (the Asahi low-level firmware), you should see some
+  output from it.
+
+- If running u-boot, you need to configure it to actually output to
+  the UART. Please refer to the M1-specific u-boot documentation on
+  how to enable the debug UART.
+
+None of the above should be too hard if you are used to any sort of
+low-level debugging, which should be the case if using a CS board.  Do
+remember that 115200n8 is the one true configuration that the CS
+firmware supports, though.